Asthenosphere

The asthenosphere is where the convection currents happen. Convection currents are when the heat from the inner core reaches out through the outer core and heats up the substance inside the asthenosphere. The hot, and now thick, but still liquid-like substance rises because it is now less dense. While this rises, it forces the other more dense cooler substance downwards, making this process start again. The asthenosphere is larger than the lithosphere.